How to Deal with Stair-Tread Glue Joint Failure
From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
They are splitting because they are drying and shrinking and the shrinkage forces are huge. So the first step is to properly dry the wood so it will not shrink further. Then when dry, you can cut a spline that you can insert in the crack and glue it into place. You may wish to actually cut a larger opening so the spline will be a bit larger and easier to handle.
Is there a stronger glue that will bridge and gap and also be stainable? No. Incidentally, a properly made glue joint has the potential to be stronger than the wood itself. You may wish to, for future work, figure out why the joint you made was not up to its potential.
From the original questioner:
The stairs are boxed in and cannot be reached from the back. Should I try to use Gorilla Glue to fill the crack and adhere to two pieces? I hear it is stainable. I am doing a test piece right now.
From contributor T:
Blow the Gorilla Glue in the gap with an air nozzle.
From contributor T:
Gorilla Glue is stainable and sticks to jatoba well. Next time, if you use Titebond, wipe the glue surface with a solvent. Jatoba appears to be oily.
From contributor J:
We have also experienced glue joint failure in jatoba and Santos. Gorilla Glue would work at the initial glue up. With these dense, oily woods, fabrication methods are very important. Glue does not fill a gap, prior to or after glue up. You could try what Gene suggested in the interim. I would remove and replace, as it is likely to only get worse.
From contributor B:
Gene's spline is most likely the best idea. I would use an epoxy glue, as this would have some gap filling properties. Another idea would be to cut butterfly keyways into the face of each tread. A decorative touch might get you by this time.
From contributor K:
Forget the Gorilla Glue. We have had no good results with Gorilla Glue or any other poly, for that matter, aside from PUR hotmelt. Jatoba usually glues fairly well but can pose some problems if the MC content is not correct. Most PVA glues do not do well over 11-12% MC, which we have found to be good because normally, you will have joint failure before the product leaves the shop, but not always. We manufacture primarily stair treads and edge glued panels and have had the same problem you are experiencing due to the MC in the wood being too high.
Gene is correct with your problem - you have moisture escaping from the end grain of your staves more than the center or tread body of your stair treads. This is causing the annular rings to shrink on the ends, opening the glue joint. I would replace, but if you want to try and field fix, a spline shim and 2 part epoxy would be my next try. Buy a good moisture meter and check every load of wood that comes into your shop prior to production. It will save you a fortune in the long run.
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